With the development of wireless information networks, typically represented by mobile communications such as satellite communication equipment, cellular phone and PHS, wireless LAN system, or vehicle mounted communication system such as ETC system of expressway or GPS, demands for an antenna used for information communication equipment have rapidly increased. Since miniaturization, weight reduction and price reduction are required for such an antenna, a molded article using a thermoplastic resin is used as a substrate for the production of an antenna (hereinafter referred to as a “substrate for an antenna”).
In the production of the antenna, it is necessary to form a conductor layer capable of serving as an electrode on the substrate for an antenna. Since means such as soldering or metal plating is employed as means for forming the electrode, the substrate for an antenna requires sufficient durability which enables prevention of deterioration of characteristics due to means for forming the electrode. In order to satisfy these characteristics, liquid crystalline polyesters have drawn attention as a thermoplastic resin used in the production of the substrate for an antenna. A liquid crystalline polyester has both a high level of heat resistance and processability, and also has low water absorption, and thus not only durability upon production of the antenna, but also durability against long-term use of the antenna becomes satisfactory.
In information communication equipments as described above, with further increase of information density, adaptability to information communication using an electromagnetic wave in a higher frequency range has been studied and thus a substrate for an antenna having more excellent dielectric characteristics has been required. As dielectric characteristics required for the substrate for an antenna, a high relative permittivity to an electromagnetic wave in a high frequency region (high dielectric property) and a low dielectric dissipation factor are considered to be important due to the following reason. A high dielectric substrate for an antenna does not cause drastic deterioration of antenna characteristics even in the case of a comparatively miniaturized antenna, and antenna gain tends to increase in the case of a substrate for an antenna having a low dielectric dissipation factor. In order to obtain a high dielectric substrate for an antenna, it is possible to use a method in which a high dielectric material is used as a filler (hereinafter may be referred to as a “high dielectric material filler”) and a substrate for an antenna is obtained from a resin composition containing the high dielectric material filler and a liquid crystalline polyester. For example, Japanese Unexamined Patent Publication No. 2004-161953 proposes tablets for antenna parts obtained by melt-mixing a composition containing 25 to 35% by volume of a liquid crystalline polyester and 65 to 75% by volume of a ceramic powder and tabletizing the mixture at a normal temperature using a tablet machine, and also discloses that tablets for antenna parts having excellent shape retention are obtained by using in combination with a wax component upon melt mixing.
The inventors of the present application also propose, as a resin composition from which a molded article having a high dielectric property and a low dielectric dissipation factor, a resin composition containing a liquid crystalline polyester having specific structural units, and a ceramic powder (see Japanese Unexamined Patent Publication No. 2006-233118).